1. Field of the Invention
The present invention relates to electric acoustic converters, and more particularly to an electric acoustic converter having a rear surface terminal. The electric acoustic converter according to the present invention can be used not only as a speaker for a mobile communication device such as a portable telephone or the like but also as a receiver thereof.
2. Description of the Prior Art
In recent years, along with a size reduction and thinning of the thickness of mobile communication devices such as a portable telephone or the like, the size reduction and thinning of the thickness are apparently promoted with respect to the electric acoustic converter used in the speaker and the receiver of the communication device.
As this kind of electric acoustic converter, Japanese Patent Application Laying-Open No. 10-164693 discloses a dynamic type electric acoustic converter. According to the patent publication, two contact piece members formed of elastic material which is bent and processed are attached on the rear surface of the electric acoustic converter. An electrode on the connector side is allowed to elastically come into contact with each of the contact points of these contact piece members (first prior art example).
Furthermore, Japanese Patent Application Laying-Open No. 11-355409 describes a dynamic type receiver in which two surface electrodes are arranged in parallel at two eccentric portions of the rear surface of the receiver (second prior art example).
Still furthermore, Japanese Patent Application Laying-Open No. 11-27777 describes an electric acoustic converter in which a positive terminal is provided on a planar upper surface of a disc-type microphone while a negative terminal is provided on a ring-like upper end surface of a metal mesh surrounding the disc-type microphone (third prior art example).
However, in the first prior art example, since bent and processed elastic material is used for the contact piece member attached on the rear surface of the electric acoustic converter, a relatively large disparity is inevitably generated in the precision of the attachment position of the contact piece member. Then, because of such disparity in the precision of the attachment position, it is difficult to set to a definite size a vertical length from the front end surface (lower end surface) of the electric acoustic converter to the contact point of the contact piece member, namely, a height measurement of the electric acoustic converter including the contact piece member. As a consequence, it has been found that the relative position relation with the electrode on the connector side provided on the set of the communication device becomes difficult to be maintained on a definite level, and the contact point pressure between the contact point of the contact piece member and the electrode on the connector side becomes difficult to be maintained on a definite level.
Furthermore, in the second prior art example, since the two parallel surface electrodes are arranged at eccentric positions of the rear surface of the receiver, it becomes necessary to set at a high precision the position relations between the electrode on the connector side provided on the set side and the two surface electrodes on the receiver side at the time of assembling this receiver in the set of the communication device. Consequently, it has been found that a complicated positioning structure is compelled to be adopted to heighten the precision of the attachment position of the receiver with respect to the set of the communication device, which leads to an increase in the cost of the communication device.
Furthermore, in the third prior art example, it has been found n that the negative terminal is provided on a ring-like upper end surface of the metal shell surrounding the disc-type microphone so that the outer configuration of the microphone becomes large because of the metal shell.